With the departure of longtime MTV Networks head Judy McGrath, Viacom chief Philippe Dauman is seizing the opportunity to solidify his grip on the company’s profit center.

After doing away with her position, Dauman is planning to further tighten his control over the cable-networks division, with one source saying the rebuilt corporate structure would be renamed Viacom Networks.

Already the company has announced that execs in charge of various MTV Networks’ divisions will now report directly to Dauman.

Viacom said it won’t name a successor to McGrath, a 30-year MTV veteran who started out as a copywriter and worked her way up the ladder.

The buttoned-down Dauman has been eager to assert his authority over the cable unit, which has lived up to MTV’s rebellious youthful image by cultivating a high degree of autonomy from its corporate parent.

For years, MTV Networks, which houses Nickelodeon, Comedy Central and VH1, has existed as a separate corporate entity with its own legal, finance and Human Resources executives, who will now report to Viacom executives.

Dauman signaled his intentions in January, when he created a new structure called Viacom International Media Networks and put MTV Networks International inside it.

McGrath’s exit comes five years after Dauman took the reins as Viacom’s chief, following the ouster of his predecessor Tom Freston, also an MTV vet.

Many expected her to exit then, but she hung on in part because Dauman wanted her to stay in order to prevent a creative exodus.

McGrath’s salary is estimated to be around $10 million, while the businesses she oversaw contributed 88 percent of 2011 pre-tax earnings, or $3.595 billion out of a total of $4.074 billion, according to Barclays Capital.

“The advertisers love her, the employees love her and she championed women in the executive suite,” said Jason Hirschhorn, former chief digital officer at MTV Networks. Last year, she placed 18th in Forbes’ closely watched 50 Most Powerful Women rankings.

Staff were scheduled to host a blowout bash for McGrath last night at media hotspot Press Lounge.

While Dauman heaped praise on McGrath yesterday, her departure was almost deemed inevitable.

One source said the two (he, a numbers guy, and she, a creative force) were involved in contract-renewal talks, but they did not go well.

“It was clear to people that he has been taking a more active role lately — running meetings or sending announcements — most things were coming from him,” said one source. “[McGrath] was like, fine, run it.”